Method and plant for the production of hot asphalt mixes with reclaimed asphalt mix material

ABSTRACT

Procedure and plant for the production of tempered bituminous mixtures with reclaimed asphalt pavement (RAP) comprises: a) Provision of RAP having a granulometry comprised between 0 and a maximum diameter; b) Processing said RAP to obtain at least two RAP fractions (one fine, another coarse); c) Subjection of predetermined quantities of said RAP fractions to a process of mixing and heating by hot gas flow such that the heating times of each fraction are adapted to the granulometry thereof, the temperature of the mixture at the end of the step being comprised between 90° C. and 120° C.; d) Blending the mixture with a predetermined quantity of bituminous emulsion supplied at a temperature comprised between 60° C. and 80° C. The temperature of the final mixture will be between 90 and 110° C.

FIELD OF THE INVENTION

The present invention relates to a procedure for the production oftempered bituminous mixtures to form the upper layers of the roadbed ofhighways and other road infrastructure utilising material recovered fromdeteriorated and/or aged layers of bituminous mixtures, renderingpossible the utilisation at a rate of up to 100% of recovered material.The invention furthermore covers a production plant for the execution ofsaid procedure.

BACKGROUND OF THE INVENTION

In general terms a bituminous mixture may be defined as a combination ofbitumen (also called asphalt) and stony mineral aggregates in presetproportions determining the physical properties thereof and, finally,the performance thereof for a given use.

The conservation of the highway assets entails planned operations ofrenovation and conservation to maintain the adequate structuraldurability and functional response thereof. In the most widespreadpavement typology, that of bituminous roadbeds, one of the most habitualand frequent operations is that of milling and removal of deterioratedand/or aged layers and the substitution (replacement) thereof by newlayers utilising newly produced bituminous mixtures.

The product generated by milling deteriorated and/or aged bituminousmixtures is habitually denominated RAP (reclaimed asphalt pavement), orMRMB (Spanish acronym for material recovered from bituminous mixtures);the former term shall be utilised hereinafter.

RAP is constituted by materials of high technical and economic value,for which reason the reutilisation or recycling thereof is desirable.

Hot procedures for the production of replacement bituminous mixtures areknown which may utilise a certain percentage of RAP (up to approximately50%), however not 100% by virtue of the fact that the high temperaturesattained during the processes of hot production (approximately between160° C. and 180° C.) deteriorate (burn′) the bitumen present in the RAP,damaging the properties thereof as a consequence.

Cold procedures for the production of bituminous mixtures withbituminous emulsion permitting the utilisation of 100% RAP are known.However, these mixtures present significant disadvantages, such as therequirement for a curing period (normally of one year as a minimum) andthe weakness of the mechanical properties thereof in the initial momentssubsequent to the laying thereof on site. For these reasons, when theseprocedures are used it is essential to add an additional wearing courseon top of the layer wherein RAP is being employed.

Moreover, in the known procedures of production of tempered bituminousmixtures, such as that described in patent ES 2 368 980 A1, theutilisation of RAP is not included.

Consequently, there currently exists a great surplus of RAP, it beingtreated as waste and having the economic and environmental disadvantagesimplied thereby.

The present invention is orientated towards the resolution of thisproblem.

SUMMARY OF THE INVENTION

An object of the present invention is to provide procedures for theproduction of bituminous mixtures having a high level of mechanical andfunctional properties and permitting a percentage of RAP recycling of upto 100%.

Another object of the present invention is to provide procedures for theproduction of bituminous mixtures permitting reducing the cost thereofwith respect to the known procedures.

A further object of the present invention is to provide productionplants for the execution of the aforementioned procedures.

In a first aspect, these and other objects are achieved through aprocedure of continuous production of bituminous mixtures from reclaimedasphalt pavement (RAP) and from a bituminous emulsion comprising thefollowing steps:

a) Provision of RAP having a granulometry smaller than a maximumdiameter D3 determined by the sieves of the shredder to be employed;b) Processing said RAP to obtain at least two RAP fractions, the maximumsizes whereof do not exceed D1 mm and D2 mm;c) Subjection of predetermined quantities of said RAP fractions to aprocess of mixing and heating by hot gas flow such that the heatingtimes of each fraction are adapted to the granulometry thereof, beingshorter and having less intensity of exposure for a fraction of smallersize (by virtue of disposing of a greater quantity of binder adhered tothe aggregate, this latter having a greater specific surface than theaggregate of greater size, in this manner preventing the deteriorationof the binder through the exposure to hot gases) than for another ofgreater size (disposing of a lesser quantity of binder, being enabled tobe exposed for a greater time to the hot gases without the binderdeteriorating), the temperature of the mixture at the end of the stepbeing comprised between 90° C. and 120° C.;d) Blending the mixture obtained in the foregoing step with apredetermined quantity of bituminous emulsion supplied at a temperaturecomprised between 60° C. and 80° C. approximately. The final mixturesubsequent to the step d) will attain a temperature of between 90 and110° C.

Advantageously, the granulometry of the first fraction is comprisedbetween 0 mm and 7 mm (and more advantageously between 0 mm and 5 mm)and the granulometry of the second fraction is comprised between 4 mmand 30 mm (and more advantageously between 5 mm and 25 mm).

The procedure admits the incorporation of virgin aggregate into themixture in order to improve the properties thereof and also, should itbe so desired, to make tempered mixtures having a rate of recovery ofRAP of less than 100%.

In the cases wherein 100% of the starting material is RAP, the quantityof bituminous emulsion is comprised between 2.5% and 3% by weight of thetotal weight of the bituminous mixture, contributing a much lowerpercentage of bitumen than that required when recycled materials are notutilised.

In a second aspect, the aforementioned objects are achieved by means ofa plant for the production of bituminous mixtures from reclaimed asphaltpavement (RAP) and from a bituminous emulsion comprising:

a) a unit for pretreatment of the material proceeding from old roadbeds,whether by virtue of milling or through the demolition of a bituminouspavement, wherein the material having more than a maximum diameter D3 mmis rejected. The fraction comprised approximately between a diameter ofD2 mm and D3 mm is fed to a shredder. The fraction smaller than D2 mm istaken directly to the output screen together with the product from theshredder. This shredder separates, with the minimum fragmentationpossible of the stony matrix, the fractions bound by the binder, that isto say that what it does in essence is ‘unstick’ the same. Thispretreatment unit may incorporate a magnetic separator preventing theinput of pickaxes or metal remains present in the material to be fed.The product from this stage obtained at the output screen is two or moreRAP fractions at ambient temperature.b) a first hopper for a first RAP fraction having a granulometry themaximum size whereof does not exceed D1 mm, a second hopper for a secondRAP fraction having a granulometry the maximum size whereof does notexceed D2 mm and a tank of bituminous emulsion, they being provided withdosing devices of the material contained therein;c) a drum dryer having an entry-end burner for the heating and mixing ofmaterials configured as a parallel flow drum, wherein the material to beheated and the hot gases proceeding from the combustion chamber thereofcirculate in the same direction, provided with two inlets of material atdiffering distances from the combustion chamber thereof;d) a first transport device (for example, a conveyor belt) disposed fortransporting preset quantities of the first RAP fraction to the inlet ofthe drum dryer most distant from the combustion chamber thereof, and asecond transport device (for example, a conveyor belt) disposed fortransporting preset quantities of the second RAP fraction to the inletof the drum dryer most proximate to the combustion chamber;e) a blender, to blend the mixture realised in the drum dryer with apreset quantity of bituminous emulsion, proceeding from the tank ofbituminous emulsion, disposed in such manner that it receives themixture realised in the drum dryer by gravity.

Advantageously, the drum dryer comprises a system of controlledrecirculation of a portion of the effluent fumes and is provided with abag filter for the treatment of the unrecycled fumes.

Advantageously, the blender comprises a system of measurement of theenergy consumption thereof permitting estimation of the humidity of thefinal bituminous mixture.

The plant may also comprise a device for raising the mixed product to aholding hopper, in this manner adapting the continuous flow of theinstallation to the discontinuous flow of the lorries. The raisingdevice may be, for example, a scraper conveyor. For long holding times,instead of a hopper, a silo of greater size, lagged and heated at thebase thereof, may be used.

The plant may also comprise a third and a fourth hopper for virginaggregate connected to a second transport device in order that thislatter may also transport preset quantities of virgin aggregate to thedrum dryer. The granulometry of the virgin aggregate will be thatrequired to obtain the final granulometry of the desired mixture, havingthe percentages determined in the working formula obtained in thelaboratory.

The third and fourth hoppers may also be utilised in an alternativemanner for a third and a fourth fraction of RAP, should it be desiredthat more than two fractions of recycled material be employed in theproduction procedure.

Other characteristics and advantages of the present invention will beappreciated from the detailed description hereinafter of illustrativeembodiments of the object thereof in relation to the figures appended.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram illustrating an embodiment of theprocedure for the production of tempered bituminous mixtures, object ofthe invention.

FIG. 2 is a schematic view with plan and elevations illustrating theprincipal components of the plant for the production of temperedbituminous mixtures, object of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The continuous procedure for the production of tempered bituminousmixtures with RAP

The steps of the procedure of the invention will be described in adetailed manner hereinafter in relation to FIG. 1.

a) The first step consists in the provision of RAP having a granulometrysmaller than D3 mm, RAP of greater than this diameter consequently beingrejected. Preferably, the granulometry will be comprised between 0 mmand a value of D3 of less than 60 mm.

b) In the second step the RAP is processed to obtain at least twofractions f1 and f2, the maximum sizes whereof do not exceed D1 mm andD2 mm, disposed in stockpiles A1 and A2. In a preferable manner, thevalue of D1 will be less than 7 mm and the value of D2 will be less than30 mm.

This treatment may be realised by means of a first operation ofshredding the RAP comprised between D2 and D3 in, for example, ashredder, and a second operation of screening the shredded material andthe remainder of the RAP (smaller than D2) to obtain said two RAPfractions f1 and f2. It is important to note that the shredder separatesthe RAP with the minimum fragmentation of the stony matrix, that is tosay that what it does in essence is ‘unstick’ the aggregate bound by thebitumen.

The treatment of this step may also include the separation of metalmaterials present in the RAP by means of magnetic separators.

Preferably, the first fraction f1 has a granulometry comprised between 0and 7 mm (and more preferably between 0 mm and 5 mm) and the secondfraction f2 has a granulometry comprised between 4 mm and 30 mm (andmore preferably between 5 mm and 25 mm).

At the end of the step there are thus obtained two (or more) RAPfractions at ambient temperature having two (or more) clearlydifferentiated granulometries, wherein the humidity has beensignificantly reduced. In this manner the quantity of bitumen present ineach RAP fraction may be calculated with greater exactitude, and withthis information the working formula of the final bituminous mixture andthe quantity of bituminous emulsion to be added in the fourth step maybe optimised.

c) In the third step predetermined quantities of RAP fractions f1, f2(and, as appropriate of other fractions), obtained in the foregoing stepare subjected to a process of mixing and heating by hot gas flow suchthat the heating times are shorter for the RAP fractions of smaller sizeand that the temperature of the mixture is comprised between 90° C. and120° C. at the end of this step c).

In an embodiment of the procedure, the execution of this step is carriedout by firstly feeding hoppers T1, T2, destined for RAP fractions f1, f2and provided with dosing devices D1, D2, from the stockpiles A1 and A2;secondly, supplying preset quantities of said fractions f1, f2 totransport devices, for example, conveyor belts B1, B2, carrying them totwo differentiated inlets of a drum dryer TS wherein said fractions aremixed and heated differentially, permitting in this manner a rate ofrecycling of RAP of 100%, by virtue of the reasons stated hereinbefore.

Consequently, in the procedure of the present invention, the RAP isheated directly, however being executed in such a manner as not toaffect the bitumen present therein.

The heating of the two fractions f1, f2 is carried out by contact with ahot gas flow ac (avoiding contact with the flame as occurs in thecounter-current drum dryers utilised in bituminous plants such as thatdescribed in patent ES 2 368 980 A1) and the heating time differs forthe two fractions f1 and f2, they being made to enter the drum dryer TSat different points in order to accommodate the differing granulometrythereof and, furthermore, the different quantities of binder (bitumen)in order not to affect the properties of the latter.

The fraction f2, having the coarser RAP, is introduced through the inletmost proximate to the source of hot gases ac (at the commencement of thedrum dryer TS), more time being required to transmit the quantity ofheat required to the coarser fraction. The fraction f1, having thefinest aggregate, is introduced through the inlet most distant from thesource of hot gases ac, situated at an appropriate point of the drumdryer TS such that the fraction f1 attains the temperature required atthe outlet from the drum dryer TS, comprised between 90 and 120° C.

In addition to the RAP fractions f1 and f2, this step may include anadditional fraction of virgin aggregate to improve the characteristicsof the bituminous mixture. In this case, this material would be suppliedto the drum dryer TS by means of the feeder belt B2 utilised for RAPfraction f2. The granulometry of the virgin aggregate will be thatrequired to obtain the desired final granulometry of the mixture havingthe percentages determined in the working formula obtained in thelaboratory. In an alternative manner, instead of employing virginaggregate, this step may include a third and a fourth fraction f3 and f4of RAP, should it be desired that more than two fractions of recycledmaterial be employed in the production procedure. In a preferred manner,the granulometries of the third and a fourth fraction f3 and f4 will becomprised between D1 mm and D2 mm. As appropriate, this material wouldalso be fed to the drum dryer TS by means of the feeder conveyor B2utilised for RAP fraction f2.

d) In the fourth step, the mixture obtained in the foregoing step ismixed with a predetermined quantity of bituminous emulsion supplied at atemperature comprised between 60° C. and 80° C.

The mixture f1+f2 obtained in the foregoing step is discharged into abitumen mixer or blender AM, wherein it is mixed together with a presetquantity of bituminous emulsion eb received at 60 to 80° C. from a tankT3 provided with a dosing device D3. In the present procedure, when 100%RAP is utilised as starting material, the quantity of bituminousemulsion eb is comprised between 2.5 and 3% by weight.

The bituminous mixture mb obtained subsequent to the fourth step may besupplied directly to a means of transport to carry it to the destinationthereof or be stored by means of a raising device in a holding hopper orsilo, which may be lagged and heated.

The plant for the production of tempered bituminous mixtures with RAP

An embodiment of the plant for the production of bituminous mixturesaccording to the invention will be described in a detailed mannerhereinafter utilising two RAP fractions and, as appropriate, virginaggregate, in relation to FIG. 2.

The fundamental components thereof are the following:

Pretreatment Unit 14

In a unit for the pretreatment of the material proceeding from themilling or demolition of a bituminous pavement (proceeding from agedroadbeds) the material exceeding D3 mm is rejected. The fractioncomprised approximately between D2 mm and D3 mm is fed to a shredder,whilst the fraction smaller than D2 mm is taken directly to the outputscreen together with the product from the shredder. This shredderseparates the RAP with the minimum fragmentation of the stony matrix,that is a say what it does in essence is ‘unstick’ the fractions boundby the binder. This pretreatment unit may incorporate a magneticseparator preventing the input of pickaxes or metal remains present inthe material to be fed. The product of this stage obtained at the outputscreen is two or more RAP fractions at ambient temperature. The valuesof D3 and D2 will depend on the size of the installation and on thefinal material to be obtained, habitual values being 60 mm for D3 and 30mm for D2.

Hoppers 1, 2, 3, 4

These are hoppers having control of the level and weight contained ineach thereof and independent weigh feeders for dosing the contentthereof. The hoppers 1 and 2 are destined for the storage of,respectively, the fine fraction and the coarse fraction of the RAPproduced in a unit for the pretreatment of the RAP. The hoppers 3 and 4are destined to store virgin aggregate of differing granulometry whichmay also be utilised as starting material for the production ofbituminous mixtures (either to improve the mixture with 100% RAP or formixtures having rates of recycled material of less than 100%). In analternative manner, the third and fourth hoppers may be also utilisedfor a third and a fourth fraction of the RAP, should it be desired thatmore than two fractions of recycled material be employed in theproduction procedure.

Drum Dryer 5

In a preferential embodiment this is a parallel flow (co-current) drum,driven by electric motors having a fuel oil burner (although any otherfuel may be employed such as, for example, gas). The combustion chamber6 thereof is disposed in an entry-end position and it has two inlets orrings in different positions. That most proximate to the combustionchamber 6 is destined for the coarsest RAP fraction(s) and, asappropriate, the virgin aggregate, and the most distant for the finestfraction of the RAP. This latter must be located at a point of the drumdryer 5 as distant as possible from the burner (in order to damage thebitumen as little as possible), however at a point such as to permitthat said fraction attains the required temperature at the outlet fromthe drum dryer, comprised between 90° C. and 120° C.

The configuration thereof with entry-end flame and the great lengththereof permit increasing the dwell time of the RAP fractions in orderto achieve the required transfer of heat whilst, however, preventingdirect contact of the RAP with the flame. It being a matter of aparallel flow drum moderates the extreme contacts of temperature withthe materials fed to the same. The materials and the hot air circulatein the same direction, differing from that occurring in the drum dryersof many bituminous plants and, in particular, that described in ES 2 368980 A1.

It is provided with frequency variators permitting modification of thespeed of rotation.

It is connected to a bag filter 13 having an extractor fan for thepurpose of reducing harmful emissions whilst promoting the combustion ofthe flame.

On being a matter of a parallel flow drum, less thermally efficient thana counter-current drum, it includes a system of recirculation of theeffluent fumes. That is to say, a given percentage of the exhaust fumesfrom the drum dryer 5 is not sent to the bag filter 13 but isrecirculated within the drum dryer 5 by means of a system ofrecirculation ducts and electrovalves.

The combustion gases may be mixed at the commencement of the cyclethereof: they may be combined with a portion of the recirculated gasesand another of fresh air by means of a tangential fan creating theturbulence required for homogeneous heating (the quantity of fresh airmay be adjusted). By means of this system of partial recirculation ofgases the efficiency of the drum in co-current or in parallel isimproved.

The combination of the entry-end burner (and, in consequence, theabsence of direct contact with the flame) and appropriate control of thetemperature by means of the partial recirculation of the fumes leads tothe treatment of the bitumen present in the RAP being very judicious,not damaging it and rendering possible the reutilisation thereof.

The burner of the drum dryer 5 is fed by fuel oil (although any otherfuel may be employed such as, for example, gas) by means of a pump froma tank at approximately 40° C. and it is filtered by means of in linefilters.

Transport devices 7, 8 from the hoppers 1, 2, 3, 4 to the drum dryer 5.The quantities of the RAP fine and coarse fractions required from timeto time are delivered, respectively, to transport devices 7, 8 (in theexample shown in FIG. 2 they are conveyor belts) as is, as appropriate,the virgin aggregate to the transport device 8, by means of dosingdevices (belt feeders with frequency variator and integral weighingapparatus) incorporated into the hoppers 1, 2, 3, 4, and said transportdevices carry them to the drum dryer 5. The transport device 8 isconnected with the inlet of the drum dryer 5 most proximate to thecombustion chamber 6, and the transport device 7 is connected to themost distant inlet.

Tank 10 of Bituminous Emulsion.

It is a heated and lagged cistern having sufficient capacity to storethe bituminous emulsion required for the process. It is connected to afrequency variator driven pump, governed by means of a control system(PID) based on the readings of a flowmeter, to supply the bituminousemulsion to the blender 9.

Blender 9.

The blender 9 receives the flow of material egressing from the drumdryer 5 and the bituminous emulsion from the tank 10 at a temperaturecomprised between 60 and 80° C.

The blender 9 is disposed beneath the drum dryer 5 in such manner thatit receives the mixture of the RAP fractions (and, as appropriate, ofvirgin aggregate) by gravity, the final mixture attaining a temperaturecomprised between 90 and 110° C. It is consequently a matter of adisposition differing from that of the plants of tempered bituminousmixtures such as that described in ES 2 368 980 A1.

The blender 9 includes a system of measurement of the energy consumptionin order to estimate, utilising appropriate correlation tables, thehumidity of the final mixture. This parameter is fundamental because, inorder to ensure adequate compaction when laying on site it is necessarythat the humidity of the mixture ranges between 0.5 and 1%.

The installation provides for the possibility of adding water to theblender in order to achieve the desired humidity in the final mixture.

Devices 11, 12 of Evacuation of the Bituminous Mixture.

The bituminous mixture egressing from the blender 9 is carried to aholding hopper 12 by means of a raising device, such as, for example, aslat conveyor 11.

Although the present invention has been described in connection withvarious embodiments, it may be appreciated from the description thatvarious combinations of elements, variations or improvements may be madethereto and falling within the scope of the invention defined in theclaims attached.

1. A continuous procedure for the production of tempered bituminousmixtures from reclaimed asphalt pavement and from a bituminous emulsion,wherein the procedure comprises the following steps: a) Provision of RAPhaving a granulometry comprised between 0 and D3 mm; b) Processing saidRAP to obtain at least two RAP fractions, the maximum sizes whereof donot exceed D1 mm and D2 mm; c) Subjection of predetermined quantities ofsaid RAP fractions to a process of mixing and heating by hot gas flowsuch that the heating times and the intensity of exposure of eachfraction are adapted to the granulometry thereof, being shorter for afraction of smaller size than for another of greater size, thetemperature of the mixture at the end of the step being comprisedbetween 90° C. and 120° C.; d) Blending the mixture obtained in theforegoing step with a predetermined quantity of bituminous emulsionsupplied at a temperature comprised between 60° C. and 80° C.approximately, the final mixture subsequent to the step d) attaining atemperature of between 90 and 110° C.
 2. The continuous procedure forthe production of tempered bituminous mixtures according to claim 1,wherein the rate of recovered material is 100%.
 3. The continuousprocedure for the production of bituminous mixtures according to claim1, wherein in step b there is obtained a first RAP fraction having agranulometry comprised between 0 mm and D1 mm, and a second RAP fractionhaving a granulometry comprised between D1 mm and D2 mm.
 4. Thecontinuous procedure for the production of tempered bituminous mixturesaccording to claim 1, wherein in step b the maximum size of the firstfraction D1 is smaller than 7 mm, preferably smaller than 5 mm.
 5. Thecontinuous procedure for the production of tempered bituminous mixturesaccording to claim 1, wherein in step b the maximum size of the secondfraction D2 is smaller than 30 mm, preferably smaller than 25 mm.
 6. Thecontinuous procedure for the production of tempered bituminous mixturesaccording to claim 1, wherein when utilising 100% RAP as startingmaterial, the quantity of bituminous emulsion is comprised between 2.5%and 3% by weight of the total of the bituminous mixture.
 7. Thecontinuous procedure for the production of tempered bituminous mixturesaccording to claim 1, wherein the material input into step c alsocomprises a predetermined quantity of virgin aggregate.
 8. Thecontinuous procedure for the production of tempered bituminous mixturesaccording to claim 1, wherein the material input into step c alsocomprises a third and a fourth RAP fraction, should it be desired thatmore than two fractions of recycled material be employed in theproduction procedure.
 9. The continuous procedure for the production oftempered bituminous mixtures according to claim 1, wherein step ccomprises a system of recirculation of a portion of the effluent fumesand a system of filtration for the treatment of the unrecycled fumes.10. The continuous procedure for the production of tempered bituminousmixtures according to claim 1, wherein the step d comprises a system ofmeasurement of the energy consumption thereof permitting estimation ofthe humidity of the final bituminous mixture and a system of addition ofwater to regulate the humidity of the final bituminous mixture.
 11. Aplant for the production of tempered bituminous mixtures from reclaimedasphalt pavement (RAP) and from a bituminous emulsion wherein the plantcomprises: a) a unit for pretreatment of the material proceeding fromold roadbeds wherein the material exceeding D3 mm is rejected and thefraction comprised approximately between D2 mm and D3 mm is fed to ashredder, whilst the fraction smaller than D2 mm is taken directly to anoutput screen together with the product from the shredder, the productobtained at the output screen being two RAP fractions at ambienttemperature; b) a first hopper for a first RAP fraction having agranulometry the maximum size whereof does not exceed D1 mm, a secondhopper for a second RAP fraction having a granulometry the maximum sizewhereof does not exceed D2 mm and a tank of bituminous emulsion, theybeing provided with dosing devices of the material contained therein; c)a drum dryer having an entry-end burner for the heating and mixing ofmaterials configured as a parallel flow drum, wherein the material to beheated and the hot air proceeding from the combustion chamber thereofcirculate in the same direction, provided with two inlets of material atdiffering distances from the combustion chamber thereof; d) a firsttransport device disposed for transporting preset quantities of thefirst RAP fraction to the inlet of the drum dryer most distant from thecombustion chamber thereof, and a second transport device disposed fortransporting preset quantities of the second RAP fraction to the inletof the drum dryer most proximate to the combustion chamber thereof; e) ablender, to blend the mixture realised in the drum dryer with a presetquantity of bituminous emulsion proceeding from the tank of bituminousemulsion, disposed in such manner that it receives the mixture realisedin the drum dryer by gravity.
 12. The plant for the production oftempered bituminous mixtures according to claim 11, wherein thetransport devices and are conveyor belts.
 13. The plant for theproduction of tempered bituminous mixtures according to claim 11,wherein the drum dryer comprises a system of recirculation of a portionof the effluent fumes and a filter for the treatment of the unrecycledfumes.
 14. The plant for the production of tempered bituminous mixturesaccording to claim 13, wherein the filter for the treatment of theunrecycled fumes is a bag filter.
 15. The plant for the production oftempered bituminous mixtures according to claim 11, wherein the blendercomprises a system of measurement of the energy consumption thereof,permitting estimation of the humidity of the final bituminous mixture.16. The plant for the production of tempered bituminous mixturesaccording to claim 11, wherein the required means are provided for theaddition of water to the blender to achieve the humidity desired in thefinal bituminous mixture.
 17. The plant for the production of temperedbituminous mixtures according to claim 11, wherein the plant includesdevices for the raising and storage of the final bituminous mixture. 18.The plant for the production of tempered bituminous mixtures accordingto claim 11, wherein the plant also comprises a third and a fourthhopper connected to the second transport device such that the latter mayalso transport preset quantities of the material stored in the third andfourth hoppers to the drum dryer.
 19. The plant for the production oftempered bituminous mixtures according to claim 18, wherein the thirdand fourth hoppers are destined to store virgin aggregate.
 20. The plantfor the production of tempered bituminous mixtures according to claim18, wherein the third and fourth hoppers are destined to store a thirdand a fourth fraction f3 and f4 of the RAP, should it be desired thatmore than two fractions of recycled material be employed in theproduction procedure.